Ask a member of the dojo what the line up procedures are. In our dojo, it's simple because we do not line up according to rank. If they don't ask, and if I see a visitor standing back to line up in a "second" line I waive them up to the main line. And the only place in our dojo that's "reserved" is during seminars when our sensei will sit all the way to the left of the line. And he doesn't care if a day one newbie is sitting next to him and the next person is a yondan or godan.